This invention relates to apparatus and method for varying the input rate of data into a system in accordance with primary power line frequency variations. More particularly, the present invention relates to apparatus and method for reducing teleprinter printing errors that are due to primary power line frequency variations.
Operation of a teleprinter machine without readout or printing errors, caused by primary power frequency variations, requires that the primary power line frequency be maintained constant within certain defined limits determined by machine design and specified by the machine manufacturer. The typical requirements specified by one teleprinter machine manufacturer is a primary power line frequency of 50 Hz or else 60 Hz with a tolerance of plus or minus 0.45 Hz. Such line frequency control is primarily necessary in order that the rotational speed of the teleprinter drive motor remain within a predetermined synchronized relationship with the data rate input to the teleprinter machine. In the normal teleprinter applications, the primary power supplied to the machine is generally obtained from commercial electric power station sources and as such is maintained within the relatively close frequency tolerances. Operation of the teleprinter machine under these conditions is therefore generally satisfactory. Some teleprinter machines are manufactured with governor controlled drive motors. These machines are more tolerant to primary power line variations of both frequency and voltage.
There is, however, an ever increasing application of teleprinter machines in operational environments where commercial electric primary power is not available and where the machines must operate from locally generated primary power. One such application is aboard ocean going ships. In many of these applications even governor controlled machines prove to be either unsatifactory in operation or pose a potential reliability problem. In remote locations where teleprinter machines are operated from locally generated primary power which is not or cannot be closely frequency regulated, printing errors result. Many times the cause of these printing errors is not known and much time and effort is expended in trying to track down the source of the errors. And of course, if the locally generated primary power commences to operate at a frequency that falls within the manufacturers specifications, the problem disappears and the cause of the printing errors is not found.
In the past, in certain applications the data rate into a system was controlled as a function of the rotational speed of the teleprinter drive motor by using electrooptic sensors to sense drive motor speed. Although this electrooptic system tends to compensate for any condition which could cause the rotational speed of the drive motor to change, it requires special modification of the teleprinter machine to incorporate the electrooptical speed sensors. This, of course, requires that a special machine be supplied by the manufacturer or that the teleprinter machine be modified either by the communications system supplier or the user.
In view of the foregoing, it should now be understood that it would be desirable to provide an improved system that would solve the above and the other problems.
Accordingly, one of the objects of the present invention is to provide a control system which is all electronic in operation and does not require modification to existing available teleprinter machines.
Another object of the invention is to provide a control system wherein the frequency of the primary power line is continuously monitored and the rate at which data is supplied to the teleprinter machine is variably controlled as a function of the frequency of the monitored primary power line.
Yet another object of the present invention is to provide a method of modifying the data rate supplied to a system as a function of the frequency of the primary power to the system in a simple and reliable manner that has the versatility of being usable with many different machines.